Joule-Thomson effect cooling devices, commonly referred to as cryostats, are well known in the art to produce cryogenic temperature levels. The cryostats may be employed to maintain radiation sensing devices at the extremely low temperatures required. Examples of conventional Joule-Thomson effect cryostats may be found in U.S. Pat. Nos. 2,991,633, 3,095,711, 3,353,371, 3,415,078 and 3,431,750.
In order to achieve a rapid initial cool-down, large coolant or refrigerant flows are required in conventional cryostats. Only a fraction of this cool-down flow is, however, needed for steady state operation of the cryostat. Thus, a cryostat designed to meet the initial cool-down flow requirements would be inherently inefficient during steady state operation, while a more efficient steady state flow design would have an excessively long cool-down period.
Since in many cryostat applications the coolant or refrigerant flow is limited by the available supply, techniques have been developed to provide sufficient cool-down flow without providing excessive steady state flow. While certain self-regulating flow control mechanisms have been developed for cryostats, these mechanisms, which have been either thermal-mechanical, electro-mechanical, or chemical in nature, have been rather complicated, overly complex and often prone to operational difficulties. All rely upon external forces, thus consuming energy such as electrical power and all include at least some moving parts. In some cases the basic cooling characteristics of the cryostat have been altered by the flow regulating mechanism.